I-Beams for Rooftop Equipment Support
A little while back, we took a look at several rooftops with solar panels installed on top of the roofs. In most of those specific cases shown, those solar panel systems didn’t use I-beams as a support for the framework or purlins underneath of the i-beams. Instead, they took shortcuts and used lighter weight type supports that set the solar panels closer to the roof system.
Today, in contrast, we’re going to look at an example of a rooftop support system where steel I-beams are used to support equipment with lighter overall weight but more concentrated loads. Beam systems like this are often used to support rooftop equipment like HVAC condenser units on the roof. People can generally install HVAC condenser units in their backyards, but it works a little better in some ways to put the HVAC condenser up on the rooftop where it’s out of the way.
Yard space in Washington DC is valuable, so if you put the HVAC condenser right in the backyard, it takes more space away from the limited outdoor space. It’s more useful, in most cases, to get the HVAC condenser up on the rooftop, but to put an HVAC condenser on a rooftop it needs the infrastructure. The power, condensate drain, refrigerant lines, and control wiring must all be run up to and through the rooftop in most cases.
Penetrations, for services, through a roof can be done properly, but unfortunately most roofing contractors don’t know how to do this basic type of installation properly and they often end up messing the roof up when simply installing a pathway for these elements to run through the roof. We’ve talked about this in past articles and described proper methodologies for installation of roof penetrations. It’s an important concept that every roofer should be trained on.
You can see examples of the roof penetrations in the same photographs that we will look at today when we look at the steel supports that lift these HVAC units above the rooftop membrane. The picture below shows two oxidized and deteriorating steel I-beams spanning above a standing seam and metal roof. The parapets at the sides of the roof are made of a double wide brick masonry and that knee wall or parapet wall which extends above the roof is clad on the sides with roofing membrane and then topped with a coping which caps the masonry parapet to protect it from water entry at the near horizontal upper surface.
The next picture below shows that connection point between the steel I-beams in the parapet, more closely. There are important principles, not only about how other elements of the roof should be built with regards to the HVAC installations, such as the service penetrations, but also how things that are more structural in nature like the i-beams should connect to the parapet wall.
Here, the contractor who installed this did it improperly and didn’t set the I beams on top of the parapet correctly. I-beams need to be isolated from a dielectric perspective. They also should have a resilient barrier between the I-beam and the metal coping of the parapet. However, sheet metal is definitely one of the most common building materials used for modern coping systems.
Also, as you can see in the picture below there’s lots of salvaged scrap historic bricks laying on top of the parapet coping. Those bricks should be removed. Often while working on many rooftops here in Washington DC will find scattered old bricks laying around. These bricks should not be set directly on top of sheet metal because they have a moisture differential and are much more absorbent to moisture than the adjacent sheet metal which leads to pinholing and oxidation and accelerated deterioration of the sheet metal.
This coming week, we’ll take another look at a different roof with a similar rooftop unit, set in a different context. One of the differences of the roof that we’ll look at in this coming week is that that particular roof has ductwork that runs and connects to the HVAC unit on top of the rooftop. The ductwork on top of the roof can be particularly problematic and we’ll talk about some of the reasons why ductwork can both solve some problems but create new problems that need to be addressed separately or in addition to the HVAC installation.
We provide this information here on our blog, and our website, to help our customers and future clients, and we recommend every building owner in DC who values the longevity of their roof (and their investments) and building use a contractor who values the simple and important principles of proper roof construction like Dupont Roofing DC. Our company specializes in flat roofing here in Washington DC and we’re happy to help building owners of almost all types.
Learn more about our company and the proper techniques of working with roofing on historic buildings in Washington DC here on our blog at DupontRoofingDC.com, and you can call us at (202) 840-8698 and email us at dupontroofingdc@gmail.com. We are happy to help and at least talk through options.
